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United States Patent |
6,002,552
|
Leung
|
December 14, 1999
|
Adaptive loading/unloading suspension
Abstract
A head gimbal assembly includes an adaptive loading/unloading suspension
with an aerodynamic compensation mechanism formed with or attached to the
load beam. The compensation mechanism causes a variable and programmable
dynamic gram load to be applied on the suspension such that a low gram
load is achieved at the time of dynamic head loading, thus significantly
minimizing or totally eliminating head-to-disk contact. The variable
suspension gram load feature can be combined with an air slider bearing
design to achieve optimal flying height performance and cost
effectiveness. Such combination provides the air bearing design with an
additional degree of freedom to achieve a more uniform flying height and
improved altitude sensitivity than under a constant preload.
Inventors:
|
Leung; Chak M. (Palo Alto, CA)
|
Assignee:
|
Read-Rite Corporation (Milpitas, CA)
|
Appl. No.:
|
232901 |
Filed:
|
January 19, 1999 |
Current U.S. Class: |
360/75; 360/244.9; 360/254; 360/254.2; 360/255.1; 360/294.7 |
Intern'l Class: |
G11B 005/48; G11B 021/02 |
Field of Search: |
360/75,103-105
|
References Cited
U.S. Patent Documents
4996616 | Feb., 1991 | Aoyagi et al. | 360/104.
|
5612841 | Mar., 1997 | Johnson | 360/104.
|
Primary Examiner: Cao; Allen T.
Attorney, Agent or Firm: Kallman; Nathan N.
Parent Case Text
This application is a division of Ser. No. 08/847,076 filed Jun. 12, 1997.
Claims
What is claimed is:
1. A method for loading and unloading a suspension formed with a load beam,
relative to a rotatable storage medium comprising:
rotating said storage medium;
automatically altering a pressure profile acting on an underside of said
load beam when the storage medium is rotating, by an aerodynamic
compensation mechanism defined on said underside, wherein said underside
faces said storage medium;
such that a variable dynamic gram load is applied to said suspension for
attracting the suspension toward the rotating storage medium.
2. The method according to claim 1, further including the steps of loading
the suspension in three stages comprising:
an initial loading stage;
a speed loading stage; and
a final loading stage.
3. The method according to claim 2, wherein said initial loading stage
includes the steps of:
rotating the storage medium at a low speed; and
loading the suspension onto the magnetic medium in a substantially vertical
direction.
4. The method according to claim 2, wherein said speed loading stage
includes rapidly accelerating the rotation of the storage medium.
5. The method according to claim 2, wherein said final loading stage
includes gently accelerating the rotation of the storage medium.
6. The method according to claim 2, wherein said three loading stages are
effectuated by programmable means.
7. The method according to claim 2, including the step of rotating the
storage medium for a predetermined period of time before final loading to
allow moving air for cleaning a read-write head secured to the load beam.
8. The method according to claim 2, further including the step of unloading
and parking the suspension in a cage.
9. The method according to claim 2, wherein said initial loading stage
includes self-loading the suspension with a preload ranging from zero gram
load to approximately below full gram load at operating conditions.
10. The method according to claim 3, further including the step of allowing
said storage medium to rotate for a predetermined period of time before
said final loading stage to allow air moving a support element carrying a
head and said storage medium to clean said head.
11. The method according to claim 4, wherein said speed loading stage
includes accelerating the rotation of the storage medium to a speed in
excess of approximately 1000 rotations per minute.
12. The method according to claim 4, wherein said speed loading stage
includes accelerating the rotation of the storage medium to a speed in
excess of approximately 100 inches per second.
Description
FIELD OF THE INVENTION
The present invention relates to disk drives and in particular to a disk
drive having a self-loading/unloading suspension.
BACKGROUND OF THE INVENTION
Presently known magnetic disk drives typically include magnetic storage
disks and head suspension assemblies having air bearing sliders on which
magnetic transducers are disposed. The air bearing sliders in a rigid disk
drive fly above the disk surface. In such disk drives, it has been
customary to start and stop the operation by a contact start/stop (CSS)
process. One design objective of conventional magnetic disk drives is to
cause most of the wear to occur at the slider/disk interface during the
start and stop stages. Minimal wear during the start and stop stages is
crucial but is often difficult to achieve.
A prerequisite to the CSS process is that the surface of the magnetic disk
be roughened to a degree sufficient to prevent high stiction that causes
the air bearing slider and the disk to adhere while the disk is not in
operation. Moreover, in order to meet the demand for increased areal
density, efforts have been made to minimize the head flying height, which
requires smoother disks.
In light of these design objectives attempts have been made to decrease the
slider size and to design new loading/unloading mechanisms for avoiding
contact start/stop. Conventionally, a constant gram load is provided to
the head suspension for loading the magnetic head to the disk. The gram
load acts to counterbalance the effect of the air bearing lift force.
However, when the air bearing lift force is removed, the head contacts the
disk, thus generating wear and debris, and compromising data integrity,
which could eventually lead to a head crash.
Dynamic head loading/unloading mechanisms have been designed to maintain an
acceptable flying height of the head over the disk. U.S. Pat. Nos.
5,289,325; 5,237,472; 5,469,314; and 5,486,964 to Morehouse et al. are
exemplary of a rigid disk drive with a dynamic head loading/unloading
apparatus. The disk drive includes a rotary actuator having a lift tab
that extends asymmetrically from the end of the load beam. The free end of
the lift tab cooperates with a cam surface on a cam assembly to provide
dynamic loading and unloading of the slider while imparting a roll to the
slider as it is loaded to and unloaded from the disk.
While these dynamic loading/unloading mechanisms may have solved certain
concerns associated with prior static loading/unloading mechanisms, they
still suffer from several drawbacks. The dynamic loading/unloading
mechanisms have relatively complex designs, and they require a very
tightly controlled loading angle. In addition, the loading/unloading cam
prevents the optimization of the z-height of the suspension, that is the
distance between the suspension mounting surface and the disk surface.
Furthermore, under a constant preload, the flying height of some slider air
bearing designs, e.g., twin rail taper flat, is not uniform, but is
typically lower at the inner diameter (ID) of the disk than at the outer
diameter (OD). The radial dynamic loading on a ramp forces the slider to
develop an air bearing with a severe initial roll increasing the
likelihood of a head crash. In addition, the ramp loading scheme lacks the
precision control intrinsic in a finely controlled rotational speed and
acceleration of the disk.
Conventional disk drives are altitude sensitive. As the altitude increases,
the flying height decreases so that the air bearing force could counteract
the constant preload.
SUMMARY OF THE INVENTION
It is an object of the present invention to substantially reduce, if not
eliminate the CSS process in head loading/unloading mechanisms.
It is another object of the present invention to provide a compensation
mechanism whereby a self-adjusting suspension automatically adapts to the
various positions of the slider relative to the disk, so as to maintain
the head flying height substantially uniform across the entire disk
surface.
It is still another object of the present invention to provide a
compensation mechanism whereby the self adjusting suspension accounts for
changing environmental conditions.
According to the present invention, an aerodynamic compensation mechanism
is secured to or formed within the load beam. The compensation mechanism
causes a variable and programmable dynamic gram load to be applied on the
suspension such that a low gram load is achieved at the time of dynamic
head loading, thus significantly minimizing or totally eliminating
head-to-disk contact. The variable suspension gram load feature can be
combined with the air slider bearing design with optimal flying height
performance and cost effectiveness. Such combination will provide the air
bearing design with an additional degree of freedom to achieve a more
uniform flying height and improved altitude sensitivity than under a
constant preload.
The suspension of the present invention can be implemented with
conventional manufacturing techniques with minimal changes to the
suspension design, hence minimizing the creation of undesirable
resonances. The suspension minimizes debris generation and power
consumption. The cleanliness of the disk plays an essential role in disk
drives and particularly those using optical data reading and recording
media.
By using the self loading suspension of the present invention it is
possible to increase the z-height tolerance of the entire head stack as
well as of the individual head. Each head will have a substantially
independent z-height which tightly matches its corresponding disk surface.
The present suspension simplifies the assembly process and improves the
manufacturing throughput. In addition, the self loading suspension could
position the slider directly over the disk before the air bearing
develops, thus minimizing the initial roll during the development of the
air bearing.
The self-loading suspension eliminates the radial movement of the slider
and allows the head to come down vertically during the operating loading
process, which is the same direction for which the air bearing is designed
for an on-track read/write operation.
The high precision motor controller for the disk can be utilized to create
an optimal RPM (revolutions per minute) acceleration schedule. This, in
turn, creates an optimized loading that minimizes the initial loading time
and further creates a gentle increase in the final stages of the dynamic
gram load to result in an extremely gentle loading and unloading stages
for reaching the desired operating conditions.
BRIEF DESCRIPTION OF THE DRAWING
The invention will be described in greater detail with reference to the
drawing in which:
FIG. 1 is a perspective view of a suspension including an aerodynamic
device according to the present invention;
FIG. 2 is a side view of the suspension of FIG. 1 shown positioned above a
data storage medium;
FIG. 3 is a cross-sectional view of the suspension and the aerodynamic
device of FIG. 1 taken along line 3--3;
FIG. 4 is an enlarged view of FIG. 3 showing air flow past the aerodynamic
device and the various forces applied to the suspension;
FIG. 5 is an enlarged view of a slider secured to the suspension such as
shown in FIGS. 1 and 2, illustrating the various forces applied on the
slider;
FIG. 6 is a graph plotting the data storage medium rotational speed in RPM
during the suspension loading/unloading process;
FIG. 7 is a graph plotting the flying height variation between the inner
diameter (ID) or outer diameter (OD) of the data storage medium when the
suspension is submitted to a fixed preload (or gram load) as experienced
in the prior art;
FIG. 8 is a graph plotting the aerodynamic gram load (DGL) variation
generated by the suspension of FIG. 1 between the ID and the OD of the
data storage medium;
FIG. 9 is a graph plotting the flying height of the slider bonded to the
suspension of FIG. 1 between the ID and the OD of the data storage medium;
FIG. 10 is a perspective view of a suspension including an aerodynamic
device according to another embodiment of the present invention;
FIG. 11 is a side view of the suspension of FIG. 10 shown positioned above
a data storage medium;
FIG. 12 is a cross-sectional view of the suspension and the aerodynamic
device of FIG. 10 taken along line 12--12;
FIG. 13 is a perspective view of a suspension including an aerodynamic
device according to another embodiment of the present invention;
FIG. 14 is a side view of the suspension of FIG. 13 shown positioned above
a data storage medium;
FIG. 15 is a cross-sectional view of the suspension and the aerodynamic
device of FIG. 13 taken along line 15--15;
FIG. 16 is a perspective view of a suspension including an aerodynamic
device according to another embodiment of the present invention;
FIG. 17 is a side view of the suspension of FIG. 16 shown positioned above
a data storage medium;
FIG. 18 is a cross-sectional view of the suspension and the aerodynamic
device of FIG. 16 taken along line 18--18;
FIG. 19 is a perspective view of a suspension including an aerodynamic
device according to another embodiment of the present invention;
FIG. 20 is a side view of the suspension of FIG. 19, shown positioned above
a data storage medium;
FIG. 21 is a cross-sectional view of the suspension and the aerodynamic
device of FIG. 19 taken along line 21--21;
FIG. 22 is a perspective view of a suspension including an aerodynamic
device according to another embodiment of the present invention;
FIG. 23 is a side view of the suspension of FIG. 22 shown positioned above
a data storage medium;
FIG. 24 is a cross-sectional view of the suspension and the aerodynamic
device of FIG. 22 taken along line 24--24;
FIG. 25 is a perspective view of a suspension including an aerodynamic
device according to another embodiment of the present invention;
FIG. 26 is a side view of the suspension of FIG. 25 shown positioned above
a data storage medium;
FIG. 27A is a cross-sectional view of the suspension and the aerodynamic
device of FIG. 25 taken along line 27--27;
FIG. 27B is a cross-sectional view of the suspension and an alternative
aerodynamic device of FIG. 25 taken along line 27--27;
FIG. 28 is a front view of the suspension of FIG. 1, illustrating the
loading and unloading process, according to the present invention, and
showing a cage in which the suspension is parked; and
FIG. 29 is a top plan view of the suspension shown parked in the cage of
FIG. 28.
Similar numerals refer to similar elements in the drawing. It should be
understood that the sizes of the different components in the Figures may
not be in exact proportion, and are shown for visual clarity and for the
purpose of explanation.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIGS. 1, 2 and 3 illustrate a head suspension assembly formed with a head
gimbal assembly (HGA) 10, comprising an adaptive suspension 12, a flexure
15 and an air bearing slider 16 secured to the flexure 15. In the
embodiment illustrated herein the term "adaptive" implies flexibility,
self-adjustment, automatic adjustment, external programmability, with the
ability to have numerous loading/unloading schemes that are customizable
to specific applications, and other features that optimize or improve the
aerodynamic performance of the HGA 10 and that allow the head suspension
assembly to compensate for disk radius effects, and to further compensate
for atmospheric condition changes. The HGA 10 may be used with various
types of storage drives, including but not limited to magnetic, optical,
or magneto-optical drives. The slider 16 carries a read or write element
18 such as a magnetic transducer, as is shown in FIG. 1, or any other
suitable assembly, for example an optical assembly for reading and/or
writing data on the disk 11. The slider 16 will also be referred to as a
support element. While the slider 16 is illustrated as being secured to
the free end of a load beam 20, it should be clear that in other
embodiments the support element or slider 16 may be positioned at a
different location along the length of the load beam 20.
The load beam 20 is secured at a rear end to a base plate 22 and at its
forward end to the flexure 15. Two side rails 24, 25 provide added
rigidity and stability to the load beam 20.
An inventive feature of the present invention is to alter the pressure
profile generated by the air flow pattern along the underside 21 of the
load beam 20 facing the disk 11. This feature is achieved by forming an
aerodynamically shaped device on the underside 21. As used herein, the
device may be formed separately from the suspension 12 and then bonded
thereon; or alternatively it may be formed integrally within the
suspension.
FIGS. 1, 2 and 3 illustrate an exemplary aerodynamic device 26 that alters
the air flow pattern along the underside 21 of the otherwise smooth
surface of the load beam underside 21 to generate either a positive
pressure or sub-ambient (e.g. negative) pressure onto the suspension 12.
The device 26 acts as a compensation mechanism that cooperates with the
air flow generated by the rotation of the disk 11 to account for the air
bearing and the suspension preload. As used herein the preload is a
constant bending force defined by the bending of the load beam 20 as is
well known in the art. In existing technology the preload is equated to
the operating or static gram load (SGL).
The aerodynamic performance of the device 26 depends upon its geometrical
shape, its distance from the disk 11, its skew angle relative to the load
beam, and the disk velocity. By changing the design and orientation of the
device 26 it is possible to create a different dynamic gram load (DGL)
profile (to be defined later) across the entire surface of the disk.
The device 26 shown in FIGS. 1 through 3 represents a first exemplary
suspension design according to the present invention. The device 26 has a
ring-like shape and is defined by an oval wall 33 that encloses a cavity
35. The device 26 may be made of the same material as the load beam 20,
such as stainless steel. Alternatively, the device 26 may be made of
another suitable material, such as ceramic or plastic. The device 26 is
secured to the underside 21 of the load beam 20 by adhesive bonding or
welding, for example. While the device 26 will be described as a separate
device that is added and secured to the suspension 12, it should be clear
to those of ordinary skill in the art that the device 26 may be formed as
an integral part of the suspension 12 by deforming (or forming) the load
beam to simulate the aerodynamic shape and performance of the device 26.
In the present example, the device 26 has a closed ring configuration, for
instance oval, and has its major axis AA coincide with the axis of
symmetry of the load beam 20, such that in an ideal case, the skew angle
between these two axes is substantially zero. This reduces the off-center
or skewed masses and residual bias torques, which benefits the on track
and seeking operation of the head assembly. This skew angle may also be
finite to change the DGL profile across the disk 11. In another embodiment
the minor axis of the device 26, which is perpendicular to the major axis
AA, may be aligned with the major axis of the load beam 20. It should be
clear that the device 26 may have different configurations. For instance,
the device 26 may be circularly shaped. In addition, a plurality of
devices 26 may be formed at the underside 21.
The thickness of the wall 33 may vary with the intended application of the
suspension 12. The height (H) of the wall 33 is such that the device 26
does not touch the disk 11 in operation, thus defining a clearance between
the wall 33 and the disk 11. The device 26 could weigh about 10 milligrams
and could generate about 1 gram of dynamic gram load (DGL). The device 26
may be located at any section of the load beam 20, provided it satisfies
the aerodynamic performance requirements as described herein.
In a conventional device the total gram load (also indicated by F.sub.NET)
acting on the suspension is defined by the following equation (1):
Total Gram Load=F.sub.NET =SGL+F.sub.U -F.sub.L, (1)
where F.sub.U is the force acting on the side of the suspension facing away
from the disk; and F.sub.L is the force acting on the opposite side of the
suspension (i.e., facing toward the disk). F.sub.U is typically the
ambient pressure force, and is equal in magnitude to F.sub.L. As a result,
the Total Gram Load is equal to SGL.
FIG. 4 illustrates the air flow past the suspension 12 and the various
forces applied to the suspension 12. The above equation (1) applies
equally to the suspension 12. However, the forces F.sub.U and F.sub.L are
not equal, since a dynamic gram load (DGL) is generated by the aerodynamic
device 26, when the disk and the suspension are in relative motion. In
this embodiment, DGL is defined as the difference between F.sub.U and
F.sub.L, i.e., (DGL=F.sub.U -F.sub.L) resulting in the following equation
(2):
Total Gram Load=F.sub.NET
=SGL+(F.sub.U -F.sub.L)
=SGL+DGL. (2)
In a specific embodiment where SGL equals zero, the total gram load equals
DGL.
As the velocity of the disk 11 increases the device 26 causes DGL to
develop further and to attract the suspension 12 toward the disk 11. DGL
results from the sub-ambient pressure developed by the aerodynamic shape
of the device 26.
A small dynamic gram load (DGL) enables a partially developed air bearing
to stabilize over the disk at a relatively elevated flying height. As a
result, it is now possible to eliminate the angled loading ramp since the
head is no longer loaded by launching it down an angled ramp, but may
rather be "dropped" onto (i.e., allowed to fall under the action of
gravity), or positioned over the disk 11. As a result of the elimination
of the loading ramp and cam, the adaptive suspension 12 permits the
achievement of a more compact disk to disk spacing than can be achieved by
conventional designs. By using the present invention it is alternatively
possible to eliminate the loading ramp all together, which may further
simplify the drive design and optimize the flying head performance.
Referring to FIG. 5, the resulting net force (Fnet) transmitted from the
load beam 20 to the slider 16, via the flexure 15, is equal to the air
bearing pressure integrated over the air bearing surface of the slider 16.
As further defined by the following equation (3), the net force (Fnet) is
related to a dynamic gram load (DGL) which provides the necessary
compensation to maintain a head 14 (FIG. 1) at a substantially uniform
flying height or some other optimal flying height profile across the
entire surface of the disk 11:
F.sub.NET =static gram load (SGL)+dynamic gram load (DGL). (3)
FIG. 6 is a graph plotting the rotational speed of the disk 11 in
revolutions per minute (RPM) during the adaptive suspension load/unload
process. The loading process includes three stages: (I) the initial
loading stage; (II) the speed loading stage; and (III) the final loading
stage.
Stage I--The Initial Loading
The Initial loading stage spans between time t.sub.0 and t.sub.1, during
which period an aerodynamic interaction between the disk 11 and the load
beam 20 is initiated in preparation for speed loading. As the disk 11
starts to rotate or move, the head 14 can be loaded vertically onto the
disk 11 instead of radially along a ramp. Vertical loading refers to the
loading of the head 14 substantially in the direction in which the air
bearing force is expected to develop. The ability of the suspension 12 to
be vertically loaded onto the disk 11 is important in that it allows the
slider 16 to develop an air bearing with minimal roll, which enhances the
development of the air bearing and allows it to develop faster. As an
example, the period (t.sub.1 -t.sub.0) of the initial stage may vary
between 10 ms and 100 ms.
At time t.sub.0 the disk 11 is rotated at a relatively low angular speed,
for example between 10% and 50% of full speed. In conventional CSS disk
drives, the head is typically loaded and/or unloaded at the inner diameter
(ID) of the disk 11, and therefore the access of the OD data tracks is
delayed. In other conventional drives, the head is typically loaded and/or
unloaded at the OD of the disk 11, and therefore the access of the ID data
tracks is delayed. In addition, conventional designs may not permit data
tracks to be located in the loading/unloading zone, whether at the ID or
the OD of the disk.
The present invention enables data tracks to be located at any position
across the disk 11, including the loading/unloading zone (at the ID or OD
of the disk 11) due to the gentleness of the loading process in general.
At time t.sub.1 the slider 16 will be hovering over, or close to the OD
tracks of the disk 11, thus allowing fast access to these OD tracks. Once
the initial loading stage is completed at time t.sub.1, the suspension 12
is said to have been activated dynamically, which will enable the speed
loading to be completed in a relatively predictable fashion.
While it is a stated object of the present invention to substantially
reduce, if not eliminate CSS process in head loading/unloading mechanisms,
it should be understood that the present invention is compatible with CSS
devices. In other words, the aerodynamic device 26 and the other
aerodynamic devices described herein may be used in conjunction with CSS
designs. As an example, in a CSS mode of operation, the initial loading
stage (i.e., Stage 1) is done in the CSS loading zone, which is typically
at the ID of the disk 11, when the air bearing has formed. Thereafter,
upon completion of the initial loading phase, the head 14 may be moved to
a position above approximately the destination data track, at which
location the remaining loading stages: the speed loading stage, and the
final loading stage occur. In the CSS mode of operation the static gram
load is lower than the full operation gram load. As a result, the take off
velocity of the air bearing would occur at a lower speed of the disk 11,
thus reducing wear at the head/disk and improving reliability.
In conventional dynamic loading disk drives, the head is loaded at the OD
of the disk. However, due to angled ramp loading, this loading zone is not
used for data storage. The gentleness of the loading process of the
present adaptive load/unload suspension 12, permits the elimination of the
angled ramp all together, and the head 14 may be loaded at any track on
the disk 11, between the ID and OD. As a result, it is now possible to
increase and to optimize storage onto the disk 11.
During this initial loading stage and the subsequent speed loading and
final loading stages, the device 26 generates a dynamic gram load force
(DGL) on the slider 16 attracting it toward the disk 11. The net force
(Fnet) acting on the slider 16 is equal to the sum of DGL and SGL. During
the non-operating condition of the disk 11, the preload (or SGL) on the
suspension 12 is equal to Fnet. According to the present invention the
preload can be finite or even infinitesimal.
Since the initial loading stage of the head 14 is very gentle, a drive
utilizing the compensation mechanism 26 of the present invention may be
used with various types of data storage media. For example, the head 14
has a higher level of tolerance to uneven disk topographies. In addition,
the dynamic loading of the head 14 substantially reduces, if not totally
eliminates startup stiction, and is also compatible with drives operating
at high speeds, for example at speeds that exceed 1000 rotations per
minute (RPMs), such as 4500 RPMs. In one example, the disk 11 has an
operating linear speed at the innermost data track of 100 inch per second
or higher.
Stage II--Speed Loading
Speed loading spans between time t.sub.1 and t.sub.2, and includes a very
rapid acceleration of the disk RPM in order to minimize the overall
loading time to a point where the flying height at time t.sub.2 is about
two to ten times the final operational flying height (FH) of the slider
16. The actual range of flying height in this stage depends on the air
bearing design and topography of the disk 11. This rapid speed loading
ability enhances the overall disk drive response. As an illustrative
example, a portable (or laptop) computer typically includes a power
conservation feature which enables it to go to a sleep mode, which slows
down or even stops the disk 11 in order to conserve power. Every time the
active mode is resumed in a conventional portable computer the dynamic
head loading sequence slows downs the system response. The present
invention improves the system level response and reduces the power-on
access time. In one embodiment the speed loading stage causes the disk 11
to accelerate to a speed in excess of approximately 100 inches per second.
Stage III--Final Loading
During this final loading stage the disk 11 has a very gentle RPM
acceleration that gently brings the head (14) flying height, pitch and
roll to operating conditions. Consequently, due to the gentleness of this
stage, the HGA 10 can complete the head loading in a very reliable
fashion, with a wide ramp angle tolerance even if used with a loading
ramp, and enables the head loading/unloading to occur over data tracks.
If a preload (SGL) were imparted to the load beam 20, the SGL could be
smaller than the DGL. If a ramp were used during loading, less wear is
induced on the ramp and the suspension 12 due to the smaller preload
force. Also the ramp design tolerance will be less critical for the
aerodynamic performance of the slider 16 because the final loading is
still substantially dominated by the generation of the DGL.
At elevated altitude conditions, air density decreases causing ambient
pressure to decrease, and resulting in a lower adaptive gram load.
Consequently, for the same head, the total gram load at an elevated
altitude is lower than the total gram load at sea level. This causes a
significant reduction of the slider flying height altitude sensitivity in
conventional air bearing designs. It is believed that the present adaptive
loading/unloading scheme substantially compensates for altitude variations
and provides the air bearing design with an additional degree of freedom
to achieve a more uniform flying height and improved altitude sensitivity
than under a constant preload.
FIG. 7 illustrates a prior art flying height profile of a twin rail taper
flat suspension relative to the ID and OD of the disk 11. This profile
illustrates the significant non-uniformity between the flying heights at
the OD tracks and the ID tracks, as the relative velocity of the head
increases, i.e., toward the OD tracks. Such non-uniformity is due in part
to the fact that the preload (fixed gram load or static gram load) is not
compensated.
FIG. 8 illustrates the compensation DGL profile relative to the ID and OD
of the disk 11. Generally, a lower disk speed at the ID generates a lower
DGL, and a higher disk speed at the OD generates a higher DGL. The slower
velocity at the ID (inner diameter) of the disk tracks allows the slider
16 to fly higher above the disk surface due to the lower DGL. Similarly,
the higher velocity of the disk OD (outer diameter) tracks allows the
slider 16 to be attracted toward the disk surface due to the higher DGL.
As a result, and as illustrated in FIG. 9, the effect of the preload (SGL)
is automatically compensated so that the slider 16 flies at a
substantially uniform and optimal flying height above the disk surface.
In one embodiment, the loading process may be programmable by customizing
the rotational speed (i.e., RPM) and the acceleration of the disk for
optimal air bearing design by means of a microprocessor control and
feedback circuit (not shown). In another embodiment, since the slider 16
flies in proximity to the disk 11, the disk 11 is allowed to rotate for a
predetermined period of time before final loading to allow the moving air
to clean the slider (16) air bearing surface by removing dust or other
particles. This feature is particularly important for optical disk drive
applications where dust can interfere with the path of the optical beam
and degrade the signal.
FIGS. 10-12 illustrate an HGA 50 according to another embodiment of the
present invention. The HGA 50 is generally similar in function and design
to the HGA 10, except that it includes a different device 52. The device
52 has a generally similar elliptical contour to that of the device 26,
and further includes a centrally open cap 53 that defines a cavity 55 with
the underside 21 of the load beam 20 and the upright wall 33 of the device
52.
In one embodiment the wall 33 extends from the underside 21. While the cap
53 is illustrated as having a centrally located opening 57 it should be
clear that the cap 53 may have two or more openings that are optimally
patterned and positioned to achieve the desired system performance. The
opening 57 may have any desirable geometrical shape. In this particular
example the opening 57 is shown as being elliptically shaped. However, in
another embodiment the opening 57 may be circularly shaped.
FIGS. 13-15 illustrate an HGA 60 according to another embodiment of the
present invention. The HGA 60 is generally similar in function and design
to the HGA 10, except that it includes a different device 62. The device
62 has a closed loop ring shaped configuration and defines a cavity 64
with the underside 21 of the load beam 20. This example illustrates the
fact that the aerodynamic device 62 may have various shapes and is not
limited to those specifically disclosed herein.
FIGS. 16-18 illustrate an HGA 80 according to another embodiment of the
present invention. The HGA 80 is generally similar in function and design
to the HGAs described herein, and includes a differently shaped device 82.
The device 82 is U-shaped, and defines a cavity 84 with the underside 21
of the load beam 20.
For the purpose of illustration, a rotary actuator platform is described.
FIGS. 19-21 illustrate an HGA 90 according to another embodiment of the
present invention. The HGA 90 is generally similar in function and design
to the HGAs described herein, and includes a device 92. The device 92 is
formed of at least two bars 92A, 92B that are preferably symmetrically
disposed relative to the major axis of the load beam 20. The device 92
provides a suitable open channel 94 between the two bars 92A, 92B for
creating the desired DGL. The length of the bars vary with the size of the
suspension 12 and the application for which the HGA 90 is designed.
Depending on the specific application, the length of the bars 92A, 92B may
be different and the channel 94 may not be symmetrical relative to the
suspension axis. In the present example the channel 94 converges toward
the slider 16.
FIGS. 22-24 illustrate an HGA 100 according to another embodiment of the
present invention. The HGA 100 is generally similar in function to the
HGAs described herein, and includes a device 102. The device 102 is solid
and generally cube shaped, though alternative shapes can be used. The
device 102 is preferably symmetrically disposed relative to the major axis
of the load beam 20. The dimensions of the device 102 vary with the size
of the suspension 12 and the application for which the HGA 102 is
designed.
FIGS. 25, 26, 27A, 27B illustrate an HGA 110 according to another
embodiment of the present invention. The HGA 110 is generally similar in
function to the HGAs described herein, and includes an device 112. The
device 112 has a special aerodynamic design, which in this case is foil
like, to clarify that the invention may be implemented with various custom
shaped devices whose shapes are not expressly disclosed herein. In this
example, the device 112 is preferably symmetrically disposed relative to
the major axis of the load beam 20, though an asymmetrical placement or a
symmetrical shape also may be used. The dimensions of the device 112 vary
with the size of the suspension 12 and the application for which the HGA
112 is designed. The device 112 may be formed as an integral part of the
load beam 20 by deforming the load beam 20.
Stage IV--Unloading and Parking
The unloading and parking stage of the suspension 12 will now be described
in relation to FIGS. 6, 28 and 29. When the power to the disk 11 is turned
off at time t.sub.3 (FIG. 6), the disk 11 slows down, the suspension 12
automatically separates the slider air bearing surface from the disk 11
due to the reduction or the elimination of the dynamic gram load (DGL),
since the DGL is a function of the disk rotation. Once the disk 11 slows
down, the suspension 12 tends to return to its static position above the
disk 11, thus separating the slider 16 from the disk 11. This is
illustrated by position (1) of the suspension 12 in FIG. 28.
The suspension 12 is then rotated at a fast speed, and is caused to ride
onto a ramp 206 forming part of a parking cage 208, to position (2). The
suspension 12 is then rotated further so that the ramp 206 guides the
suspension 12 to a resting position in a parking station 210, at position
(3), where it is retained by friction and motion constraints at the top
and bottom of the suspension 12.
Since the DGL is negligible at the end of the unloading stage, and in the
specific embodiment in which SGL is very small or infinitesimal, Fnet is
very small, and therefore the ramp 206 may be eliminated since the
suspension 12 is capable of moving in a plane substantially parallel to
the disk surface. In such an alternative embodiment the parking station
210 is located in substantially the same plane at position (1) of the
suspension.
The cage 208 may be made of metal, plastic or any other suitable material
that does not emit contamination, such as aluminum. The parking station
210 acts as a stop for the suspension 12, and holds it in the parking
position (3) by means of a limiter plate 211 until reloaded unto the disk
11. The cage 208 further includes a block 212 that connects the cage 208
to other cages in a head stack assembly (not shown). In the CSS drive
configuration, the head unloading will occur in the reverse sequence of
the loading process.
It should be understood that the geometry and dimensions described herein
may be modified within the scope of the invention. The geometries of the
various aerodynamic devices may be modified depending upon the disk drive
operating characteristics. Other modifications may be made when
implementing the invention for a particular environment. Further, the
dynamic loading/unloading operation of the suspension 12 may be fully
programmable and related to the disk rotational speed and acceleration. In
addition, it is also possible to use one or more aerodynamic devices on a
single load beam 20. While the present invention has been described in
connection with a rotary actuator, the inventive concept is equally
applicable to other types of actuators.
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